Gold (Au) nanoshells are nanoparticles usually composed of a dielectric core, typically silica, coated with an ultrathin Au layer. These nanoparticles show interesting optical and chemical properties for the applications of surface-enhanced Raman spectroscopy (SERS) sensor, surface plasmon resonance (SPR) sensor, drug delivery, biomedical imaging and cancer therapeutics among others.
Reducing symmetry of Au nanoshells geometry shows interesting properties. It is possible to excite different plasmon modes in these particles when compared to standard particles. These particles show angle dependent plasmon resonance. This unique property may lead to a new class of optically active nanoparticles that can be manipulated by applied static or frequency dependent electric, magnetic, or optical fields. The particles enhance the electric field intensity coming out of the particles when compared to fully covered particles, i.e. particles whose symmetry has not been reduced.
Several groups have developed and demonstrated reduced-symmetrical nanoshells such as nano half-shells, nanocups, nanomoons and nanoeggs for SERS applications. Reduced-symmetrical nanoshells have been prepared before in various ways including electron-beam evaporation (EBE) and electroless plating. By these methods, the reduced-symmetrical structures of nanoshells, such as nanoaperture or nanotip, are usually oriented randomly or with their aperture downward, which obviously limits the molecular binding to the electric field enhanced regions in SERS applications. The Raman enhancement factors differ from place to place on a substrate because of the random orientation of reduced-symmetrical structures.
U.S. Pat. No. 6,660,381 describes a method for the fabrication of composite particles containing metal shell layers, i.e. a partial metal coverage. This fabrication method does not allow good control of the orientation and the geometry of the open-nanoshells.
WO2006135393 shows a method and a system for optimized surface enhanced Raman scattering comprising a support with on top nanoparticles having a shell surrounding a core. The local electromagnetic field around complete shells is lower when compared to the local electromagnetic field around the open-nanoshells.
WO2002059226 describes the fabrication of metal nanoshells having partial coverage of a substrate.
JP2006198641 describes an ion-beam processing method for forming nano-order convex portions.
Y. B. Zheng et al (J. of Non-crystalline Solids 352, 2006, p 2532-2535 describe the fabrication of ordered nanoring arrays for nanoscale optical sensors. This fabrication method does not allow good control of the geometry of the open-nanoshells.
J. Liu et al (Jap. Journ. Of Appl. Phys. 45 (22), 2006 p L582-L584 describe the fabrication of 2-dimensional arrays of hollow metal nanoshells on a substrate. This fabrication method does not allow good control of the geometry of the open-nanoshells.
M. A. Correa-Duarte et al (Advanced Materials 2005 (17), p 2014-2018) describe a method to fabricate asymmetric nanoshells with/without a core. This fabrication method does not allow good control of the orientation of the open-nanoshells.
Lu et al. (Nano Lett. 5 (1), 2005, p 119-124) present the fabrication of Au moon structures for the enhancement of a local electrical field at the edge area. This fabrication method does not allow good control of the orientation of the open-nanoshells.
J. C. Love et al (Nano Lett. 2 (8) 2002, p 891-894) describe the fabrication of silica core particles covered with Au on a substrate. This fabrication method does not allow good control of the orientation and the geometry of the open-nanoshells.